Open in Visual Studio Code” fails because /var/lib/flatpak/app/ is stripped from editor path

Environment:
- SteamOS
- GitHub Desktop: io.github.shiftey.Desktop Flatpak, system install
- VS Code: com.visualstudio.code Flatpak, system install
- GitHub Desktop has default filesystem=host permissions

Reproduction from inside GitHub Desktop sandbox:

FAILS:
flatpak-spawn --host \
com.visualstudio.code/current/active/export/bin/com.visualstudio.code \
"$HOME"

Error:
Failed to execute child process
“com.visualstudio.code/current/active/export/bin/com.visualstudio.code”
(No such file or directory)

WORKS:
flatpak-spawn --host \
/var/lib/flatpak/app/com.visualstudio.code/current/active/export/bin/com.visualstudio.code \
"$HOME"

Cause appears to be formatPathForFlatpak() stripping
/var/lib/flatpak/app/ before spawnEditor() calls flatpak-spawn --host.

Search the Python code for formatPathForFlatpak() and spawnEditor(), then inspect how the VS Code Flatpak path is transformed before flatpak-spawn --host runs. Reproduce the failing and working commands from the issue on SteamOS with the listed Flatpak installations. Done means Open in Visual Studio Code uses the executable path that includes /var/lib/flatpak/app/.

Written by the indexing model from the issue text.